Microwave device



May 24, 1949.

E, Filed Aug. 10, 1943 R. lA. BRADEN MICROWAVE DEvI cE 2 Sheets-Sheet 1- nuentor QE/ml (Ittorneg R. A. BRADEN May 24, 1949.

MICROWAVE DEVICE 2 Sheets-Sheet 2 Filed Aug. 10, 1943 r TMV W m ma@ j a E 4 m rs 4 Patented May 24,A 1949 MICROWA-V E DEVICE Rene A. Braden, Princeton, N. J., assignor to Radio Corporation .of America, a corporation of Delaware Application August 10, 1943, Serial No. 498,127

10 Claims.

This-invention relates generally to microwave apparatus and more particularly toA microwave modulation devices employing a-plurality of c'avity resonators coupled together to provide multiresonant tuning characteristics.

In ultra-high frequency receiving systems it` modulator device comprising a toroidal cavity resonator and means for generating arr-electronbeam which is modulated by variations in electric field intensities established within the cavity resonator by input signals and'` local oscillations coupled thereto. Signals from an ultra-high frequency antenna are coupled to thecavity resonator by means ofv a coupling` loop1 extendingA into` the' cavity resonator. Similarly, a sourceh of local oscillations of a frequency different from the input signal frequency is' coupled to the cavity resonator by means of a second coupling loop extending intok said resonator. The electron beam is generated by a conventional thermionic cathode and passes through apertures in the constricted center portion of the cavity resonator to an anode electrode disposed adjacent one of said apertures. The cavity resonator is tuned to the mid-frequency between the signal frequency and the local oscillation frequency.

A second cavity resonator tuned to the same mid-frequency is coupled tothe first cavity resonator by means of fixed or adjustable coupling means. The coupling should be fixed, or adljustable, to the value which causes thel system as a whole to be resonant to both signal and oscillator frequencies. The two cavity resonators may be enclosed withink a single evacuated envelope, or the second cavity resonator' mayy bodiments and modifications gf the invention dis'- closed herein havex been limited to rst detector circuits suitable for ultra-high.- frequency receivers merely for thel purpose of 'simplifying the explanatio'n thereof. Broadly, the inventio'nimay` be applied to various other' radio tuning and modulation circuit elements-where multi-frequency or band-pass characteristics are desired.

Among they objects ofthe invention are to provide ari-improved methodof andv means for applying signals of a plurality of frequencies to acavity. resonator. Another objectv of the invention is to provide anv improved method o'f andy means` for applying signals of bothr input signal frequencies and local oscillation frequencies to* a cavity resonator typelultra-high-frequencyv detector. Another object of thel invention is to provide-an improved cavity resonator type ultrahigh-frequenc'y modulation device comprising an evacuated envelope enclosingV a cavity resonator tuned to an operating frequency wherein an electric field is established for modulating electrons.' passing through alconstricted portion of said cavity resonator, and meansv for coupling to said cavity resonator a second!` cavity resonator tuned! to the same operating frequency in a manner providing resonanc'el at twov operating frequencies. Another object of the invention is toprovide an improved ultra-high-frequency modulation device including two cavity resonators tunedi to the same or different operating frequencies and coupled together to provide a-multi-reso'nan't device, and meansfor modulating an electron beam by directing saidy beam through one of said cavity resonators.

A further object of the invention is toV provide an improved ultra-high-frequency first detector circuit for anl ultra-high-frequency superheterodlyne receiver whereinwb'and-pass' tuning characteristics are provided by a plurality of cavity resonators coupledto a cavity resonator enclosed within an evacuated envelope, wherein: an electric field may bel established within the enclosedl cavity resonator tomodulate an electron beamLv in accordance with input signal frequency signals and frequencies fromv a source of local oscillations. An additional object of the invention is to provide means for coupling a plurality of cavity resonators tuned to the same or diiferent operating frequencies to provide multi-frequency or band-pass characteristics in at least oney ofof said cavity resonators.

The invention will be further describedI by're'ierenc'e to theA accompanying drawings of vvhicl-rl Figure 1 is a schematic circuit diagram of oneiff embodiment thereof; Figure 2 is a schematic circuit diagram of a second embodiment thereof; Figure 3 is a schematic circuit diagram of a modification of the embodiment disclosed in Fig-- ure 2; Figure 4 is a schematic circuit diagram of a third embodiment of the invention and Figure 5 is a schematic circuit diagram of a modi flcation of the embodiment of the invention disclosed in Figure 4. Similar reference characters are applied to similar elements throughout the drawing.

Referring to Figure 1, an evacuated envelope l encloses a cathode 2, heated by a heater element 3, and an anode electrode 4. Connections are brought out through the evacuated envelope for the cathode heater and anode electrodes. A conventional toroidal cavity resonator, having apertures 5 at its center constricted portion, is disposed between the cathode 2 and anode l in such a manner that the electron beam between the cathode and anode electrodes passes through the apertures 5 of the cavity resonator A first coupling loop 'l extending into the cavity resonator 6, is connected to a receiving antenna 8. A second coupling loop 9, also extending into the cavity resonator 6, is connected to a source oi' local oscillations I0. A third coupling loop II, extending into the cavity resonator t, is coupled to a second cavity resonator I2 which is disposed outside of the evacuated envelope I. The coupling to the second cavity resonator I2 is provided by a coupling loop I3 extending therein. The coupling loops Il and I3 within the rst and second cavity resonators 6, l2, respectively, are coupled together by an adjustable coupling device I4 illustrated herein as a pair of parallel disposed coupling loops I5, I6. It should be understood that any other adjustable means of coupling the loops I i, i3 in the two cavity resonators may be employed to equal advantage. The second cavity resonator I2 is tuned to resonate at the frequency of the source of local oscillations I0. If desired, both cavity resonators may be tuned to the mid-frequency between the signal and oscillator frequencies.

The effect of coupling the two cavity resonators 6, I2, by means of the coupling circuit described, is to provide a device which responds efficiently at both signal input and local oscillation fre quencies. The effect is quite similar to providing relatively large mutual coupling between conventional resonant circuits tuned to the same or slightly different operating frequencies. Since the first cavity resonator 6 is thereby caused to have two degrees of freedom, an electric field will be established therein at both the signal input and local oscillation frequencies, and will modulate the electron beam accordingly. Therefore, a modulation frequency equivalent to the sum or difference between the signal input and the local oscillation frequencies may be derived from the anode electrode 4 and applied, through an inductively coupled output circuit, to the input of a conventional intermediate frequency amplifier, not shown.

Figure 2 discloses a second embodiment of the invention which is similar to that described in Figure 1, but wherein the two toroidal cavity resonators, 6, I2 respectively, disposed in parallel planes, are enclosed within a common evacuated envelope I. The cavity resonators may be tuned halfway between the signal input and the local oscillation frequencies. The two resonators in tersect at the points I'I and include a common aperture I8 to provide a desired degree of coupling therebetween. The size of the common aperture I8 between the cavity resonators 6, I2 will determine the coupling between the two resonators and thus the band-pass characteristics of the device. The rst cavity resonator includes apertures 5 at its constricted center portion which permit an electron beam to pass from the cathode 2 to the anode 4 in the same manner as described heretofore in Figure 1. The operation of the devices of Figure 1 and Figure 2 are identical except that in the latter device fixed coupling is provided between the two cavity resonators. The center portion of the device of Fig. 2 may be supported by radial arms extending therefrom across the aperture I8 to the junction I'I of the outer resonator shells 6, I2.

Figure 3 is a modification of the embodiment disclosed in Figure 2 wherein the toroidal cavity resonators intersect only at the point I9 of the outer peripheral portions of the first and second cavity resonators 5, I2 respectively. rEhe two cavity resonators 6, i2, respectively, are tuned to the signal input and local oscillation frequencies, or to the mean of said signal and oscillator frequencies, and the structure of the device is identical in all other respects to that of the device described in Figure 2.

lt should be understood, however, that the coupling loops l and 9 from the signal input circuit 8 and the source of local oscillations I0, respectively, may be coupled to either the second cavity resonator I2, or to the rst cavity resonator (i as indicated by the switches SI, S2. The essen tiai diiference between the modifications disclosed in Figures 2 and 3 is in the overall shapes thereof, since the operating electrical characteristics of both devices are substantially identical and coupling is obtained between the two resonant cavities l2 respectively, by means of the common aperture I8 therebetween in the same manner as described in Figure 2.

Figure 4 is similar to the device described in Figure 1 with the exception that separate tuning means have been provided for the signal input and local oscillation coupling circuits. The evacuated envelope I includes a cathode 2, heater element 3 and anode electrode il, and a first toroidal cavity resonator 6 having apertures at the constricted center portion wherein the apertures 5 are in the path of the electrons from the cathode to the anode electrode li.

The source of local oscillations I0 is connected through a coupling loop 2li to a second cavity resonator 22, which may be tuned by means of a tuning screw 23 extending therein. The second cavity resonator 22 includes an output coupling loop 24 which is connected through a conventional trombone line adjusting unit 25 and concentric transmission line 25 to an oscillator frequency coupling loop 9 extending into the first toroidal cavity resonator 6. The first and second cavity resonators Ei, 22 are tuned to a frequency midway between the signal and local oscillator frequencies, and are so coupled that there are two resonant frequencies corresponding to the signal and oscillator frequencies.

Signals derived from the antenna 8 are coupled to a third cavity resonator 2'! by means of an input coupling loop 28. The resonant frequency of the third cavity resonator 21 is adjusted to the signal frequency, and may be varied by means of an adjusting screw 29 which varies the spacing between the constricted center side walls of the toroidal cavity, thus resulting in broadened resonance at the signal frequency,

andata An output coupling` leoni-:extending into the thirdcavity resonator.. 21,l coupled, through a second trombone line adjusting unit 3|-, to the signal input coupling loop 1 in the'rst cavity resonator 6;` enclosed'c' withinrtlfe evacuated envelope l.

Figure 5 shows a typical modification of the signal input circuit of' Figure. 4,.` wherein ay bal.- ancedinput. loop 35' is connectednto the signal input loop.- 1 ofv the first. cavity resonator 6 which is enclosed within the evacuated en.- velopel-. The characteristics of the apparatus witl'i-iny the evacuated envelope I, are identical to that described in Figure..4. Thefantenna' 8T is cor-inected.v tol predetermined'. points on the: balanced'loop35 to provide effective. coupling thereto. The balanced loop circuit, 35 is tuned by means of atuning stub. 3E connected thereto at a. second predetermined point, The tuningstub 36 is tuned by means of a shorting bar 3l.

A second coupling loop 9, extending into the resonant cavity 6 within the evacuated envelope I, may be coupled to the source of local oscillations I0 in the same manner as described and illustrated in Figure 4.

Thus the invention described comprises several embodiments and modifications of a unique ultra-high-frequency modulation device employing a plurality of cavity resonators to provide multi-frequency or band-pass frequency response.

I claim as my invention:

l. Multi-resonant microwave apparatus including two resonant devices each tuned to predetermined resonant frequencies, said resonant devices being mutually coupled together, means coupled to only one of said devices for establishing therein standing waves at two different frequencies, a predetermined one of said devices being adapted to have an electric field established in a predetermined direction therein, and means coupled to only said predetermined one of said devices defining an electron beam path extending through only said predetermined device in a direction parallel to the path of said electric eldwhereby said electron beam is moduated by both of said waves.

2. Apparatus as claimed in claim 1 including means coupled to one of said devices for deriving signals from said one of said devices in response to said modulated electron beam.

3. Multi-resonant microwave apparatus including two intersecting cavity resonators mutually coupled together and tuned to be mutually lresonant at two dierent frequencies, means coupled to said resonators for establishing therein standing waves at each of said frequencies, a predetermined one of said devices being adapted to have an electric field established in a predetermined direction therein, and means coupled to only said predetermined one of said resonators defining an electron beam path extending through only said predetermined resonator in a direction parallel to the path of said electric field to modulate said beam at both of said frequencies.

4. Muti-resonant microwave apparatus including two cavity resonators mutually coupled together and differently tuned to be mutually resonant at two different frequencies, means coupled to said resonators for establishing therein standing waves at each of said frequencies, a predetermined one of said devices being adapted to have an electric eld established in a predetermined direction therein, and means coupled to only said predetermined one of said resonators defining anrelectromldeam path extendii-xgvthmuglf: only said:predeterminedfresonatemin aadireeti'cm parallel-tame patlsrronsaicltelectri'c il'eldato` moda late said beam at both of saisitfrequencies;I

5. Multi-resonant microwave' apparatusincluding two.` coaxiale` intersectix-ig cavity resonatorsA mutually coupled-together* and,I tuned: toi be' mutually resonant at time, different ,frequena cites, means coupled to said? resenatorsrfon estab;- lishin'gr therein standing wavesfatv each.. ofi saiidi frequencies, a. predtermlned one ofi said:l devices being adaptedfto haveiam electric-afieldilestablished in: a: predetermined: direction:l therein, and; means coupled: totA only; said predetermined one` ofY saidtresonators :defining an electron .bea/:rrr` path extending through-onlyvsaidipredeterminedf resonator; in':- au directioni parallel: tof the;I path; of. sa-idil electricreld tozmoldnlatersai'drbeam at both: of said. frequencies;

6i. Multi-resonant; microwave apparatus including two coaxial toroidal cavity resonators mutually coupled together and tuned to be mutually resonant at two different frequencies, means coupled to said resonators for establishing therein standing waves at each of said frequencies, a predetermined one of said devices being adapted to have an electric field established in a predetermined direction therein, and means coupled to only said predetermined one of said resonators defining an electron beam path extending through only said predetermined resonator in a direction parallel to the path of said electric eld to modulate said beam at .both of said frequencies.

'7. Multi-resonant microwave apparatus including two cavity resonators having adjacent similar portions mutually coupled together and tuned to be mutually resonant at two different frequencies, means coupled to said resonators for establishing therein standing waves at each of said frequencies, a predetermined one of said devices being adapted to have an electric field established in a predetermined direction therein, and means coupled to only said predetermined one of said resonators defining an electron beam path extending through only said predetermined resonator in a direction parallel to the path of said electric field to modulate said beam at both of said frequencies.

8. Multi-resonant microwave apparatus including two cavity resonators having adjacent peripheral portions mutually coupled together and tuned to be mutually resonant at two different frequencies, means coupled to said resonators for establishing therein standing waves at each of said frequencies, a predetermined one of said devices being adapted to have an electric field established in a predetermined direction therein, and means coupled to only said predetermined one of said resonators defining an electron beam path extending through only said predetermined resonator in a direction parallel to the path of said electric f'lld to modulate said beam at both of said frequencies.

9. Multi-resonant microwave apparatus including two resonant devices each tuned to the same resonant frequencies, said resonant devices being mutually coupled together, means coupled to one of said devices for establishing therein standing waves at two different frequencies, a predetermined one of said devices being adapted to have an electric field established in a predetermined direction therein, and means coupled to only said predetermined one of said devices defining an electron beam path extend- 7 ing through only s'aid predetermined device in a direction parallel to the path of said electric eld whereby said electron beam is modulated by both of said waves.

10. Multi-resonant microwave apparatus including two resonant devices each tuned to predetermined resonant irequencies, said resonant devices being mutually coupled together, tunable means coupled to one of said devices for establishing therein standing waves at two different frequencies, a predetermined one of said devices being adapted to have an electric field established in a predetermined direction therein, and means coupled to only said predetermined one of said devices dening an electron beam path extending through only said predetermined device in a direction parallel to the path of said electric eld whereby said electron beam is modulated by both of said waves.

RENE A. BRADEN.

8 REFERENCES" CITED The following references are of record in the" le of this patent:

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